Aeddan was supposedly
the son of Caw, the great Pictish overlord of the North. He travelled south,
perhaps with his brother Gildas and became
a pupil of St. Dyfrig at Hentland
in Ergyng, then a friend of St. Dewi. Along
with Teilo and Ysfael, Aeddan and Dewi
travelled to Mynyw (St. Davids) where Dewi founded his famous abbey. They
were at first harassed by an Irish pirate named Bwya but he was eventually
struck down and his fortress burnt to the ground.

An old tale is often
told of how, while Aeddan and Teilo were reading in the cloister at Mynyw
(St. Davids), they were called upon to replenish the monastery's fuel
stores. Annoyed at having been drawn away from their studies, the two monks
took their axes off to the woods; but found their task much easier than
expected when two tame stags aided them in carrying the wood home. There is
a well and a pool, named after Aeddan, within two miles of St. Davids and he
is patron of the church at Llawhaden in Pembrokeshire.

Later, Aeddan crossed
the Irish Sea and founded the monastery of Guernin (Ferns) in the
Emerald Isle, where he was known as Maeddog. He is said to have left his
bell behind, which St. Dewi had given him, and found it miraculously
transported to his side! Traditionally, he also helped halt the English
invasions of Britain by the use of prayer. He is, unfortunately, widely
confused with an early 7th century Bishop of Ferns of the same name and is
sometimes, wrongly, called a Bishop of
Llandaff. The true tradition appears to have been that, in old age,
he returned to his roots in Ergyng and became the fifth
bishop of that kingdom. He died around AD 608.